ATPG (Automatic Test Pattern Generation) is an electronic design automation methodology used to find an input (or test) sequence that, when applied to a digital circuit such as an integrated circuit, enables automatic test equipment (ATE) to distinguish between correct circuit behavior and faulty circuit behavior caused by fabrication defects. The generated patterns are used to test devices after manufacture, or to assist with failure analysis.
Another aspect of digital circuits to test is the frequency of test clock signals generated by clock signal generators, such as phase locked loops. If the actual frequency of a test clock signal generated by a clock signal generator is not the frequency intended to be generated, then the results of the ATPG testing may be incorrect and the test circuitry may malfunction.
Current ATPG circuits are unable to test the frequency of generated test clock signals. Instead, an additional and separate clock monitor circuit is used to test the frequency of generated clock signals. This consumes additional area. In addition, depending on the circuit layout, routing of the generated test clock signals to a separate clock monitor circuit may be difficult.
Accordingly, to eliminate the above drawbacks, development of ATPG circuits capable of testing or verifying the frequency of the test clock signals is desirable.